Creating appealing characters has been one essential desire for feature animation. One challenging aspect is the production of life-like deformations for soft tissues comprising both humans and animals. In order to provide the necessary control and performance for an animator, such deformations are typically computed using a skinning technique and/or an example based interpolation method. Meanwhile, physical simulation of flesh-like material is usually avoided or relegated to an offline process due to its high computational cost. However, simulations create a range of very desirable effects, like squash-and-stretch and contact deformations. The latter is especially desirable as it can guarantee pinch-free geometry, which is important for subsequent simulations like cloth and hair.
Although the benefits of solving the equations of the underlying physical laws for character deformation are clear, computational methods are traditionally far too slow to accommodate the rapid interaction demanded by animators. Uniform grid discretizations can be computationally efficient. However, a uniform grid cannot conform to the complicated boundary of an animated character. In order to approximate the boundary of the character closely, a high-resolution grid must be used. But using such a high-resolution grid is computationally expensive and consumes large amounts of memory, making it impractical.
Accordingly, what is desired is a framework for the simulation of soft tissues that retains the efficiency of a grid discretization, while accurately approximating the boundary of the character using a non-uniform grid cell size. In order to be useful in production, any such approach must be robust to large deformations. Additionally, what is desired is to solve problems related to character skinning, some of which may be discussed herein, and reduce drawbacks related to character skinning, some of which may be discussed herein.